Case report of an acquired factor XIII inhibitor: diagnosis and management.

A 57-year-old man presented with a spontaneous upper-extremity hematoma and compartment syndrome. The patient experienced excessive bleeding following evacuation of the hematoma, and the results of routine coagulation studies were normal. Factor XIII activity was undetectable using a photometric assay, and the presence of an inhibitor was detected with mixing studies. Bleeding was controlled with infusions of fresh frozen plasma and cryoprecipitate. Cyclophosphamide was started on the 16th hospital day, and four weekly doses of the monoclonal anti-CD20 antibody, rituximab, were begun 3 weeks later. One week after the initial dose of rituximab, the inhibitor was no longer detectable and the factor XIII level increased to 28%. After completion of the rituximab therapy, the factor XIII activity was 58% with no inhibitor present. This case illustrates the need to check for unusual defects such as factor XIII deficiency if a bleeding tendency is evident-even if routine studies are unrevealing.